The purpose of this study is to determine the role of mechanical stimulation and gastrin on the developmental patterns of enzymes which synthesize and degrade two major neurotransmitters, acetylcholine (ACh) and norepinephrine (NE), in the gastrointestinal (GI) tract. The objectives of this study are listed below. 1. To determine the role of mechanical stimulation (e.g., food) on the postweaning pattern of 4 neurotransmitter enzymes in segments of the GI tract. This will be accomplished by comparing enzyme activities in intestinal segments of rats who have undergone ileal bypass at day 21 with sham-operated controls of the same age. Enzyme activities to be assayed are choline acetyltransferase (ChAT) and acetylcholine esterase (AChE) which synthesize and degrade ACh, and tyrosine hydroxylase (TH) and monoamine oxidase (MAO) which synthesize and metabolize NE. 2. To evaluate the effect of various dosages of pentagastrin, a synthetic form of the GI hormone, gastrin, on ChAT, AChE, TH, and MAO activities. Furthermore, hormone administration will be initiated on days 14 and 21 to determine if there is an age-dependent response. Rats will be injected i.p. for seven days with 1,5,100, or 250 ug/kg pentagastrin. 3. To further characterize the role of the adrenal glucocorticoid, corticosterone, on the developmental pattern of neurotransmitter enzyme activites. This will be accomplished by creating hypo or hyper plasma corticosterone levels in subgroups of rats subjected to ileal bypass or pentagastrin treatment. All experiments will be conducted on male Sprague-Dawley rats. ChAT, AChE, TH and MAO activities will be assayed in various gut segments. Plasma and adrenal corticosterone contents will be determined in all rats. Since ACh and NE play profound roles in determining GI motility and secretion, those factors which modulate the development of their synthesis and degradation would produce obvious physiological effects.